Search results for "Spectral imaging"

Clinical evaluation of melanomas and common nevi by spectral imaging

2012

A clinical trial on multi-spectral imaging of malignant and non-malignant skin pathologies comprising 17 melanomas and 65 pigmented common nevi was performed. Optical density data of skin pathologies were obtained in the spectral range 450-950 nm using the multispectral camera Nuance EX. An image parameter and maps capable of distinguishing melanoma from pigmented nevi were proposed. The diagnostic criterion is based on skin optical density differences at three fixed wavelengths: 540nm, 650nm and 950nm. The sensitivity and specificity of this method were estimated to be 94% and 89%, respectively. The proposed methodology and potential clinical applications are discussed.

Hyperspectral system for early detection of rottenness caused by Penicillium digitatum in mandarins

2008

Abstract Nowadays, the detection of fruit infected with Penicillium sp. fungi on packing lines is carried out manually under ultraviolet illumination. Ultraviolet sources induce visible fluorescence of essential oils, present in the skin of citrus and which are released by the action of fungi, thus increasing the contrast between sound and rotten skin. This work analyses a set of techniques aimed at detecting rotten citrus without the use of UV lighting. The techniques used include hyperspectral image acquisition, pre-processing and calibration, feature selection and segmentation using linear and non-linear methods for classification of fruits. Different methods such as correlation analysis…

Active locking and entanglement in type II optical parametric oscillators

2018

Type II optical parametric oscillators are amongst the highest-quality sources of quantum-correlated light. In particular, when pumped above threshold, such devices generate a pair of bright orthogonally-polarized beams with strong continuous-variable entanglement. However, these sources are of limited practical use, because the entangled beams emerge with different frequencies and a diffusing phase-difference. It has been proven that the use of an internal wave-plate coupling the modes with orthogonal polarization is capable of locking the frequencies of the emerging beams to half the pump frequency, as well as reducing the phase-difference diffusion, at the expense of reducing the entangl…

Quantification of spatial inhomogeneity in perovskite solar cells by hyperspectral luminescence imaging

2016

Vacuum evaporated perovskite solar cells with a power conversion efficiency of 15% have been characterized using hyperspectral luminescence imaging. Hyperspectral luminescence imaging is a novel technique that offers spectrally resolved photoluminescence and electroluminescence maps (spatial resolution is 2 micrometer) on an absolute scale. This allows, using the generalized Planck’s law, the construction of absolute maps of the depth-averaged quasi-Fermi level splitting (Δμ), which determines the maximum achievable open circuit voltage (Voc) of the solar cells. In a similar way, using the generalized reciprocity relations the charge transfer efficiency of the cells can be obtained from the…

Hyperspectral terahertz microscopy via nonlinear ghost imaging

2020

Ghost imaging, based on single-pixel detection and multiple pattern illumination, is a crucial investigative tool in difficult-to-access wavelength regions. In the terahertz domain, where high-resolution imagers are mostly unavailable, ghost imaging is an optimal approach to embed the temporal dimension, creating a “hyperspectral” imager. In this framework, high resolution is mostly out of reach. Hence, it is particularly critical to developing practical approaches for microscopy. Here we experimentally demonstrate time-resolved nonlinear ghost imaging, a technique based on near-field, optical-to-terahertz nonlinear conversion and detection of illumination patterns. We show how space–time c…

2015

In this study we present a hyperspectral flying goniometer system, based on a rotary-wing unmanned aerial vehicle (UAV) equipped with a spectrometer mounted on an active gimbal. We show that this approach may be used to collect multiangular hyperspectral data over vegetated environments. The pointing and positioning accuracy are assessed using structure from motion and vary from σ = 1° to 8° in pointing and σ = 0.7 to 0.8 m in positioning. We use a wheat dataset to investigate the influence of angular effects on the NDVI, TCARI and REIP vegetation indices. Angular effects caused significant variations on the indices: NDVI = 0.83–0.95; TCARI = 0.04–0.116; REIP = 729–735 nm. Our analysis high…

Dynamics of the transition from polarization disorder to antiphase polarization domains in vector fiber lasers

2014

We demonstrate that nonlinear polarization coupling in a fiber ring laser without polarization-selective elements, subject to the effects of average anomalous dispersion, Kerr effect, and nonlinear gain saturation, can lead to the antisynchronization of spatiotemporal chaos into a wide variety of ordered laminar states of orthogonal polarization temporal domains. These antiphase polarization domains include stable lattices of soliton trains with high duty cycle at repetition rates of hundreds of MHz, as well as sparse trains of coupled dark and bright solitary waves.

Light polarization measurements in tests of macrorealism

2018

According to the world view of macrorealism, the properties of a given system exist prior to and independent of measurement, which is incompatible with quantum mechanics. Leggett and Garg put forward a practical criterion capable of identifying violations of macrorealism, and so far experiments performed on microscopic and mesoscopic systems have always ruled out in favor of quantum mechanics. However, a macrorealist can always assign the cause of such violations to the perturbation that measurements effect on such small systems, and hence a definitive test would require using non-invasive measurements, preferably on macroscopic objects, where such measurements seem more plausible. However,…

Modulational Instability and Stimulated Raman Scattering in Normally Dispersive Highly Birefringent Fibers

2001

Abstract The nonlinear interaction of two laser beams in normally dispersive highly birefringent optical fibers leads to a large set of fascinating physical effects such as modulational instability (MI) and stimulated Raman scattering (SRS). These two nonlinear phenomena have a positive role as a mechanism for the generation of short optical pulses and represent a drawback in fiber-optics transmissions. Indeed, we will show that an induced process of modulational instability may be exploited for the generation of THz train of vector dark solitons. The technique of frequency-resolved optical gating is used to completely characterize the intensity and phase of the dark soliton trains. On the …

Dissipative Polarization Domain Walls in a Passive Coherently Driven Kerr Resonator.

2021

Using a passive, coherently driven nonlinear optical fiber ring resonator, we report the experimental realization of dissipative polarization domain walls. The domain walls arise through a symmetry breaking bifurcation and consist of temporally localized structures where the amplitudes of the two polarization modes of the resonator interchange, segregating domains of orthogonal polarization states. We show that dissipative polarization domain walls can persist in the resonator without changing shape. We also demonstrate on-demand excitation, as well as pinning of domain walls at specific positions for arbitrary long times. Our results could prove useful for the analog simulation of ubiquito…